Method of detecting and repairing a structural roof damaged by subsurface moisture

ABSTRACT

A method under the title of the application, which involves generating an infrared image of a roof from an airborne position, from infrared radiation emitted by the roof in the spectral band from about 2 to about 14 microns, preferably from about 8 to 14 microns, thus locating roof portions corresponding to areas of anomalous radiation which are potentially moisture laden areas of the roof, and effecting repairs of those roof portions where the presence of subsurface moisture is confirmed by coring or other inspection procedures.

United States Patent [191 Eassella et a1.

[ Feb. 12, 1974 James J. Cavalier, Orchard Lake, both of Mich.

[73] Assignee: The Tremco Manufacturing Company, Cleveland, Ohio [22]Filed: Jan. 19, 1973 [21] Appl. No.: 325,025

[52] US. Cl 52/741, 52/514, 250/340 [51] llnt. Cl. E0411 l/66, HOlj31/50 [58] Field of Search 52/741, 514; 73/355 EM;

[56] References Cited UNITED STATES PATENTS 3,056,958 10/1962 Anderson..250/340 3,191,035 6/1965 Brumfield et al. 250/334 3 ,48 l ,087 12/1969Stafford 3,488,500 1/1970 Welti 250/334 Primary Examiner-Henry C.Sutherland [5 7] ABSTRACT A method under the title of the application,which involves generating an infrared image of a roof from an airborneposition, from infrared radiation emitted by the roof in the spectralband from about 2 to about 14 microns, preferably from about 8 to 14microns, thus locating roof portions corresponding to areas of anomalousradiation which are potentially moisture laden areas of the roof, andeffecting repairs of those roof portions where the presence ofsubsurface moisture is confirmed by coring or other inspectionprocedures.

7 Claims, No Drawings METHOD OF DETECTING AND REPAIRING A STRUCTURALROOF DAMAGED BY SUBSURFACE MOISTURE This invention relates to theroofing art and, more particularly, to a method of detecting andrepairing roof systems damaged by subsurface moisture. The invention isparticularly applicable to the large flat, and sloped roofs commonlyfound on industrial, commercial, and educationalbuildings, includingmanufacturing plants, apartments, office buildings, warehouses, schools,hospitals, and the like.

Most of these roofs are built-up roofs and will vary to some degree ontheir exact construction. Roofs are fabricated from a series ofsuperposed layers of materials on the job site. Starting from the insideout, a conventional built-up roof construction starts with a roof deckwhich could be steel, concrete, wood, wood fibres, gypsum, concreteplanks, or any one of the many other decking materials now avilable.Applied over the roof deck is a vapor barrier with the prime purpose ofpreventing moisture laden air from within the building from penetratinginto the roof system. The material used for the vapor barrier could bepolyvinyl chloride sheeting, one or several sheets of roofing felts,mopped in with hot asphalt, or one of the many other types of vaporbarriers commercially available.

Disposed over the vapor barrier is the insulation, with the primarypurpose of insulating the building, i.e., preventing heat losses in thewinter and cooling losses in the summer. Commercially availableinsulation materials include fiberboard, fiberglass, foam glass, mineralaggregate, urethane board, sprayed urethane, polystyrene, epoxy, andvarious combinations of these and other materials.

Disposed on top of the insulation is the roof membrane whichconventionally consists of a series of alternate layers of roofing feltsand a bituminous laminate. The laminates may consist of one of the manytypes of asphalt or coal-tar pitch. The felts comprise of fibrousmaterial such as asbestos, or fiberglass. They may be saturated, forexample with an asphalt or coal-tar pitch, or unsaturated, perforated orimperforate, granuled surfaced or nongranuled surfaced. The topmostsurface of the roof membrane is usually provided with a heavy mopping ofbitumen, or a coating of one or more of the various roof paints or newelastomers now on the market, such as silicone,'urethane, epoxy, orother synthetic elastomers. Where the roof is heavily mopped it may becovered with slag, gravel, marble chips, or other types of aggregate.

Moisture may infiltrate a roof system during the construction of thebuilt-up roof. Roofing materials on the job are frequently storedunprotected from the elements. Inclement weather such as rain, snow,sleet, fog, or even high humidity in the atmosphere will dampen thematerials before and during installation, resulting in built-up" wetinsulation.

Moisture may also infiltrate the roof system if the vapor barrier isomitted, not specified, damaged during construction, or damaged bymovement after construction.

As the roof membrane ages, the exposed surfaces tend to become brittleand dry through the deleterious effects of weathering, e.g. exposure toultraviolet and infrared radiation, moisture, gases, and pollutants. Inaddition, thermal movement of the various roofing components, due totemperature changes, aggravates the aging condition by exerting forcescapable of producing cracks and breaks in the roof membrane, throughwhich water may be admitted into the roofing system. The water maypenetrate the outer layer through the roofing felts, down through theinsulation, then down through the vapor barrier and into the buildingbelow. The presence of a reliable vapor barrier may prevent the waterfrom entering the building interior, but in this event, the water wouldbe trapped within the insulation of the roof system.

Moisture trapped in the roof insulation tends to proliferate throughoutthe roof system due to gravity, at mospheric conditions, and thevaporizing effect of solar heat. Vapor pressures intensify in the roofsystem with solar heat causing blisters, felt delamination, breaks,holes, etc. This enhances the already deleterious effects of weatheringand thermal movement and hastens the eventual failure of the roofsystem.

As the insulation within the roof system becomes water laden, theinsulating value of the roof insulation decreases. Even moderately dampinsulation has little insulating value. Unless and until water actuallyleaks into the interior of the building under the roof system, buildingowners generally remain unaware of the wet insulation. Wet insulationnot only fails to insulate, but when subjected to wet-dry cycles, losesadhesion to the vapor barrier on the interior side and adhesion to theroof on the outside. This creates a further problem of movement,shrinkage, and expansion of all components of the roof system since theroof membrane and insulation are not restrained.

The more devastating stage of extended wet insulation can completelydeteriorate the structural roof deck underneath, resulting in woodrotting, steel rusting, concrete spalling, and gypsum and wood fiberscrumbling. Weights from traffic, snow, standing water, etc. can cause acomplete collapse of any roof under these conditions.

In order to forestall the advancement of roof deterioration, it isnecessary to make periodic visual inspections of the roof surface todiscern anticipated sources of water entry into the roof system andvisible evidence of the actual presence of water in the insulation.Historically, these inspections have been conducted by one or more mentouring the roof looking for breaks, holes, dry exposed felts, blisters,fishmo uths, or other openings which could allow water to enter the roofsystem.

Visible earmarks of water or moisture already trapped within the roofsystems insulation include blisters, delaminated roofing felts, andsponginess underfoot.

Water or moisture which has infiltrated the roof systems insulation asdescribed above is normally not detectable by conventional visualinspection unless the deterioration has progressed to more advancedstages. Thus, a perfectly sound appearing roof may be completelysaturated. Therefore, for a complete and thorough analysis of thecondition of the roofing system, the roof membrane must be cut andopened to visually observe the extent of moisture invasion. This methodof inspection is generally known as coring, and can also be supplementedby an electrical probe, which must be verified due to the changes in theelectrical current produced by small flashlight batteries. Coring of aroof should involve, at a minimum, the cutting of cores each 20 feet inall directions with additional cores being cut to define precise areasof wet insulation.

The aforementioned technique for a thorough inspection of the roof has anumber of imperfections and inadequacies. The cutting of cores requiresmaking holes in the water-proofing roof membrane, which are potentialsituses of moisture penetration. The cutting of even the minimum numberof cores, i.e., foot intervals, is a costly, time consuming procedure.Further, there is no way of determining with any certainty the preciselocation of the wet insulation, since it is possible that the insulationmay be wet between the dry cores.

Due to the expense and time involved, proper examinations cannot alwaysbe conducted although most building owners, at a minimum, conduct orhave conducted a visual inspection of the roof. The practice of cuttingcores is either completely ignored, due to the time element, or it isminimized to only the suspected areas observed through visualinspection. As a result, areas much larger than the probable wet areaare replaced just to be sure. in some instances an entire roofing systemmay be replaced rather than spending the time and cost for a morethorough inspection. This practice can double the costs of repairing theroof system.

Another possible consequence of incomplete inspections is the risk ofmaking repairs over water damaged but undetected roof portions. Suchrepairs usually will fail prematurely forcing the owner to expendadditional monies to effect proper repairs.

Although some of these problems are minimized if all roof inspectiontechniques are utilized, the inspection falls short of adequacy due tothe guesswork inherently involved in such inspections.

It should be apparent from the foregoing discussion that the presentmethods of detecting and repairing roof systems damaged by moisture areless than satisfactory, and that there is a need for improved methodsfor accomplishing these objectives. The present invention is addressedto filling this need.

In accordance with the present invention, an entire roof can beinspected for any moisture laden areas below the surface of the roof andidentified in a matter of minutes, regardless of the size of thebuilding, through the recording of thermal imagery. More specifically,in accordance with the present invention, there is provided a method ofdetecting and repairing roof systems damaged by subsurface moisture,comprising, detecting and recording, from an airborne position, infraredradiation emitted by a roof in the range of about 2 to 14 microns inwavelengths, generating a visual image from the emitted infraredradiation, photographing the visual image to provide a permanent recordthereof, locating roof portions corresponding to anomalous radiation,confirming the presence or absence of subsurface moisture in thecorresponding roof portion and repairing those roof portions where thepresence of subsurface moisture is confirmed.

It is therefore an object of the present invention to provide animproved method of detecting and repairing a roof system damaged bysubsurface moisture.

A further object of the present invention is to provide a method ofdetecting and repairing roof systems damaged by subsurface moisture byemploying infrared imagery to detect the damaged roof areas to identifythe metes and bounds of the areas to be repaired.

These and other objects and advantages will become apparent from thefollowing detailed description of the invention which includes the bestmode presently contemplated for practicing it.

As is well known, all bodies of matter at temperatures above 0 K emitelectromagnetic radiation. The magnitude and wavelength of this thermalradiation, emitted per unit area, is a function of the temperature andemittance characteristics of the emitting body. It has been found thatthe infrared emission of black or gray bodies, at approximately 300 K(room temperature), peaks at approximately 10 microns and, in general,covers the infrared spectral region of wavelengths from above about 2microns to about 14 microns. This region embraces two bands ofwavelengths about 3 to about 5.5 microns and about 8 to about 14microns, which cover the wavelengths of most of the emitted infraredradiation.

For purposes of the present invention, it has been found that operationin the 8 to 14 micron band has been the most successful, since this bandembraces the maximum emission wavelength at about 10 microns. However,this does not preclude operating successfully within the 2 to 14 micronregion.

In practice of the present invention, the inclusion of water in the roofinsulation alters the thermal properties of the insulation, primarily,in two ways, by increasing its thermal capacity and thermalconductivity.

An increase in the thermal capacity of a roof portion will result in alag in the time it takes for that portion of the roof to show atemperature response to varying heat loads, such as occur during thedaytime due to solar radiation. Specifically, as the sun rises and aroof is subjected to an increasing heat input, the wet insulation areaswill warm at a slower rate than dry insulation areas due to theincreased heat capacity and thus appears cooler in infrared images.Conversely, after the sun sets and the roof is cooling, the wetinsulation areas will in time appear warmer than the surrounding roofareas.

An increase in the thermal conductivity of an area of a roof can bedetected from infrared imagery if there exists a thermal gradient acrossthe thickness of the roof. Specifically, if the outside air temperatureis substantially lower than the inside air temperature as in winter,then the more conductive wet areas of the roof will be characterized bya reduced temperature gradient across the thickness of the roof. Thus,the wet areas will be warmer than the surrounding roof areas and can beobserved on the infrared images as areas of increased radiation.

Visible images can be prepared which correspond to the infrared images.The visible images can be processed so that the areas of increasedinfrared radiation can appear as either lighter or darker than areas oflow infrared radiation.

In the practice of the invention, the roof to be inspected and repairedis flown over either in a helicopter or fixed wing aircraft at anelevation within the range of about 300 feet minimum for a helicopter,and about 1,000 feet minimum for fixed wing aircraft. Maximum heightwould be approximately 800 feet for the helicopter, and 1,500 feet forthe fixed wing aircraft. Although air speed will vary, generally theaverage speed for our purposes for helicopter is 50 mph, and on fixedwing aircraft, mph.

The equipment used to detect and record infrared imagery comprises aremote sensing instrument which may, for example, comprise a liquidnitrogen cooled semiconductor infrared detector placed at the focus ofan optical collector which is caused to scan the roof, as the aircraftmoves forward, by means of a rotating mirror optical system.

The detector senses consecutive scan lines across the flight path. Theelectronic signal from the detector is amplified and used to modulate aglow tube, the light from which is a visible representation of theintensity of sensed infrared energy. This light is scanned acrossphotographic film in a process which duplicates the original scanningmotion. Advancing the film duplicates the forward motion of theaircraft.

Alternatively, the amplified signal may be recorded as a digital oranalog signal, for example on magnetic tape, and then translated into avisible image on a CRT (cathode ray tube) glow tube modulator laser beamor the like. A permanent photographic record would then be made of thevisible image. To minimize the amount of equipment which must beairborne it is preferred to do no more than record the digital or analogsignal aloft and process the signal into a permanent visible record onthe ground. Even the digital or analog signal may be recorded on theground by telemetry.

Remote sensing instruments, useful in the practice of the invention, arecommercially available. Examples are Thermal Mapper LN-2LW and ThermalMapper LN3, both utilizing a l-lgCdTe detector which senses radiation inthe 8 to 13 micron spectral region. Thermal Mapper TM-LN-3 also providesfor the interchangeability of detector modules for sensing radiation inthe 0.2 to 13 micron spectral region. Both models are manufactured bythe Aerospace Systems Division, Bendix Corporation.

Coupled with the remote sensing instrument is an oscilloscope, whichserves as a monitoring device and as a data collection checkpoint. Itenables the scanner technician to make adjustments in the contrast andbrightness of a visible representation of the applied signal from thedetector. One example of the oscilloscope is the Tektronix Model No.422.

At the same time that the remote infrared sensing instrument isdetecting and recording a visible image of infrared radiation, it ishighly desirable to photograph, by conventional photographic means, thesame target or areas being scanned by the infrared sensing equipment,for use as a reference for visual interpretive information. By using thephotograph as a reference it is possible to include or exclude fromfurther consideration certain areas of anomalous radiation asidentifying potentially moisture laden areas. For example, by checkingthe actual photograph, an area of anomalous radiation on the infraredimage may be explained by a shadow, ponded water, a boiler room, variouscolors of the roof surface with varying differences in emissivity,vaporized moisture from air conditioning units, or the like. These areascan then be excluded from further consideration as potentiallysubsurface moisture laden areas.

While the thermal image generally indicates the location of ventilators,vent pipes, sumps, and expansion joints by their recognizable anomalousradiation patterns which provides suitable bench marks for preciselocation of the suspected areas of subsurface moisture laden insulationradiation, the conventional photographs serve to verify the existence ofthe bench marks.

After the anomalous areas on the photograph of the thermal imagery havebeen located, and those attrib uted to phenomena other than subsurfacemoisture eliminated from further or subjugated to secondaryconsideration, the roof is then inspected physically to confirm thepresence or absence of subsurface moisture in the remaining areas ofanomalous radiation. Since the metes and bounds of the anomalousradiation area are generally well defined in the photograph of thethermal imagery, it is necessary to cut and inspect only a very few coresamples of the roof to confirm the presence or absence of moisture. Thisexamination procedure not only confirms the presence or absence ofmoisture, but assists in making the determination of the extent of thedamage, type of construction, and the type of repair which should bemade.

Repairs can be divided into two broad categories; rehabilitation of theexisting roof system, and replacement of the roof system. It is possibleto utilize both categories on one roof. If moisture infiltration hasbeen nominal, and the insulation lends itself to breathing it may bepossible to rehabilitate the roof system in the installation ofinsulation vents to relieve the vapor pressure, and to eventually dryout the insulation. When this procedure is followed, all breaks andopenings where water had or still could penetrate the roof system, mustbe repaired and sealed tightly to preclude a reoccurrence of theoriginal problem.

Depending on the severity of the aging process, the roof may alsoreceive either a rejuvenating or penetration application, or one of thevarious surface coatings, depending on the type and/or condition of theroof involved.

Where moisture infiltration has reached a point closer to saturation,where entrapped moisture has damaged the surface of the roof, or wheredamage to the deck is suspected, it is necessary to remove the roofingsystem down either to the roofing deck or the vapor barrier, dependingon individual conditions, and replace the roof with a new roof system.Deterioration or unsafe roof decks must also be replaced.

It will therefore be seen that the present invention provides animproved method of detecting and repairing roof systems damaged bysubsurface moisture. The method not only permits a very rapididentification of potentially moisture laden areas of the roof underconsideration, but substantially reduces the amount of actual roofinspection needed to confirm the presence or absence of subsurfacemoisture and evaluate the amount of damage done by the moisture.Practice of the method also provides a clear delineation of the area ofmoisture damage, greatly simplifying estimating and specifying the areasto be replaced, thus effecting a substantial savings in time andmaterials, and the elimination of waste.

Having thus described our invention, we claim:

1. A method of detecting and repairing a roof damaged by subsurfacemoisture comprising detecting from an airborne position infraredradiation emitted from the roof in the range of about 2 to about 14microns in wavelength generating a visible image from the detectedradiation photographing the image to provide a permanent record thereoflocating roof portions of said image corresponding to areas of anomalousradiation potentially attributable to subsurface moisture confirming thepresence or absence of subsurface moisture in said roof portions andrepairing those roof portions where the presence of subsurface moistureis confirmed.

2. The method as defined in claim 1 wherein said detecting step isconducted at an elevation within the range of from about 300 to about1,500 feet above the roof.

3. The method as defined in claim 1 wherein said step of confirming thepresence or absence of subsurface moisture comprises cutting one or morecores from the roof and examining the subsurface structure for moisture.

4. The method as defined in claim 1 wherein the step of locating roofportions corresponding to said areas of anomalous radiation comprisesgenerating an actual photograph of the roof and locating on it roofportions corresponding to said areas of anomalous radiation.

5. The method as defined in claim 4 wherein said detecting step and saidstep of generating an actual photograph of the roof are both conductedat an elevation within the range of from about 300 to about 1,500 feetabove the roof.

6. The method as defined in claim 1 wherein said detecting step isconducted with respect to emitted radiation in the range of about 8 toabout 14 microns.

7. The method as defined in claim 5 wherein said detecting step isconducted with respect to emitted radiation in the range of about 8 toabout 14 microns.

1. A method of detecting and repairing a roof damaged by subsurfacemoisture comprising detecting from an airborne position infraredradiation emitted from the roof in the range of about 2 to about 14microns in wavelength generating a visible image from the detectedradiation photographing the image to provide a permanent record thereoflocating roof portions of said image corresponding to areas of anomalousradiation potentially attributable to subsurface moisture confirming thepresence or absence of subsurface moisture in said roof portions andrepairing those roof portions where the presence of subsurface moistureis confirmed.
 2. The method as defined in claim 1 wherein said detectingstep is conducted at an elevation within the range of from about 300 toabout 1,500 feet above the roof.
 3. The method as defined in claim 1wherein said step of confirming the presence or absence of subsurfacemoisture comprises cutting one or more cores from the roof and examiningthe subsurface structure for moisture.
 4. The method as defined in claim1 wherein the step of locating roof portions corresponding to said areasof anomalous radiation comprises generating an actual photograph of theroof and locating on it roof portions corresponding to said areas ofanomalous radiation.
 5. The method as defined in claim 4 wherein saiddetecting step and said step of generating an actual photograph of theroof are both conducted at an elevation within the range of from about300 to about 1,500 feet above the roof.
 6. The method as defined inclaim 1 wherein said detecting step is conducted with respect to emittedradiation in the range of about 8 to about 14 microns.
 7. The method asdefined in claim 5 wherein said detecting step is conducted with respectto emitted radiation in the range of about 8 to about 14 microns.